The present invention relates to a photographing optical system employing a non-circular lens.
Many photographing optical systems of an ordinary type use circular lenses. In the case of a miniature camera, however, the lenses are required to be as small as possible and as light in weight as possible. To satisfy these requirements, circular lenses are worked or ground to remove the portions other than the effective area portions. In the case of lenses which are to be incorporated in the photographing optical system of a camera, they can be formed as substantially rectangular since the frames of film which are to be exposed to light are rectangular.
Jpn. UM Application KOKAI Publication No. 05-11116 and Jpn. Pat. Application KOKAI No. 09-197237 disclose a lens barrel and a photographing lens system, respectively, and the lenses described in them are non-circular lenses obtained by cutting off part of circular lenses.
In the lens barrel disclosed in Jpn. UM Application KOKAI Publication No. 05-11116, a first lens section includes a non-circular lens which is obtained by cutting off the upper and lower portions of a circular lens, and the use of such a non-circular lens contributes to a decrease in the size of the lens barrel. The publication, however, does not provide a detailed description as to how the lens should be held, nor does it provide any suggestions on the holding method.
Jpn. Pat. Application KOKAI No. 09-197237, which is directed to improvements of the prior art described above, proposes a technique for reducing the number of structural components required and making efficient use of the space. According to this reference, the optical system is adjusted first and then a predetermined holding member is secured to the optical system. The invention of the reference, however, has a disadvantage that the adjustment of the lenses of the optical system is inevitably complicated. In addition, the non-circular lens usually cannot be worked with high precision at the non-arcuate outline portions, and cannot be easily held with high accuracy.
Accordingly, an object of the present invention is to propose a lens holding structure which is employed in a photographing optical system to hold a non-circular lens having an arcuate outline portion, and which is simple in structure and provided with a lens frame or the like.